In recent years, houses with less air circulation and equipped for air conditioning and heating have provided a hotbed for growth of bacteria and molds, which allows microorganisms to grow all the year. Control of bacteria or mold growth is important especially for patients who are exposed to an environment having bacteria harmful to humans and are less resistant to these bacteria with their reduced physical strength due to their diseases and for health workers who work in such an environment.
In particular, the excrement, blood, etc. from patients have high possibility of bacterial contamination. In order to secure a safe and hygienic environment, antimicrobial properties have been increasingly demanded for disposable medical supply products made of a vinyl chloride resin, such as urine bags.
In order to make these products antimicrobial, it has been practiced to add various antimicrobial agents to a vinyl chloride resin used as a raw material or to apply a synthetic resin coating containing an antimicrobial agent to the products.
It has long been known that specific metals such as silver have antimicrobial properties. The antimicrobial properties of such metals are known attributed to a trace amount of ions leached out from their surface. Known antimicrobial agents utilizing these metals include inorganic ones prepared by modifying various inorganic compounds, such as zeolite, silica gel, and hydroxyapatite, with the metals and salts of the metals with various organic acids.
These known metal-based antimicrobial agents, however, are still unsatisfactory. Besides, those using silver suffer from remarkable color change due to light, which has limited their application.
JP-A-7-196869 proposes compounding zinc oxide into a specific polymer material as antimicrobial agent. However, zinc oxide exhibits small antimicrobial effect so that substantial effects will not be produced unless it is added in a large amount.
Known organic antimicrobial agents include pyrithione and its metal salts, phenols, and organic compounds containing halogen or sulfur.
Although these organic compounds are excellent in antimicrobial properties, many of them are harmful to the human body, and they are insufficient in heat resistance and stability compared with inorganic antimicrobial agents. They tend to decompose or escape from the product to lose their effects when a vinyl chloride resin to which it has been added is heated or on contact with water or oil in use. In such situations, they also produce unfavorable effects such as coloring, generation of smell, and reduction of physical properties of the vinyl chloride resin material. These disadvantages have limited their applicability.
Therefore, it has been keenly demanded to develop an antimicrobial agent that exhibits high heat resistance withstanding the heat processing of polymer materials and high stability against water and oil, undergoes no coloration that would impair commercial value of the product, and has high safety to the human body; and a vinyl chloride resin composition exhibiting excellent antimicrobial properties by addition of the antimicrobial agent.
JP-A-58-1736 discloses use of an aromatic cyclic phosphoric ester metal salt as a nucleating agent for crystalline resins, but effectiveness of the compound as an antimicrobial agent is not described, still less suggested.